This invention relates generally to systems for the passive restraint of motor vehicle occupants and, more particularly, to cover retention in vehicular occupant restraint module assemblies.
Safety restraint systems which self-actuate from an undeployed to a deployed state without the need for intervention by the operator, i.e., "passive restraint systems" and particularly those , restraint systems incorporating inflatable bags or cushions, and the use of such systems in motor vehicles have been the subjects of much discussion as the desirability of the use of such passive restraint systems has gained general acceptance in the United States.
It is well known to protect a vehicle occupant using a cushion or bag that is inflated with gas, e.g., an "air bag" when the vehicle encounters sudden deceleration, such as in a collision. The term "air bag" is something of a misnomer, however, as during deployment the rapidly evolving gas with which the bag is filled is typically not air but rather an inert gas, e.g., nitrogen. In such systems, the air bag is normally housed in an uninflated and folded condition to minimize space requirements. In an emergency, gas is discharged from an inflator to rapidly inflate the air bag. The air bag, upon inflation, serves to restrain the movement of the vehicle occupant as the collision proceeds. In general, such air bags are commonly designed to be inflated in no more than about 45-60 milliseconds.
Vehicular inflatable restraint systems generally include multiple crash sensors generally positioned about or mounted to the frame and/or body of the subject vehicle and serve to sense sudden decelerations by the vehicle. In turn, the sensor sends a signal to an air bag module or assembly strategically positioned within the riding compartment of the vehicle to actuate deployment of the air bag. In general, the air bag provided for the protection of a vehicle driver, i.e., a driver side air bag, is typically mounted in a storage compartment located in the steering column of the vehicle. Whereas, the air bag for the protection of a front seat passenger, i.e., a passenger side air bag, is typically mounted in the instrument panel/dash board of the vehicle.
Typical occupant restraint systems make use of a module which generally includes an outer reaction housing, also commonly referred to as a reaction canister or "can". The reaction housing or can generally serves to support or contain other components of the occupant restraint module system, including what is referred to as a "air bag inflator" or, more briefly, as an "inflator", or, alternatively, as a "generator" as well as some sort of enclosure cover. The inflator, upon actuation, acts to provide the gas to inflate the air bag.
The inflator is generally either of a pyrotechnic or hybrid type. Pyrotechnic inflators generally contain a gas generating inflate the air bag. In contrast, hybrid type inflators which in material which, upon activation, generates gas which serves to addition to a body of ignitable pyrotechnic material generally contain as the primary inflation gas a stored, compressed gas which is expelled from the inflator upon proper actuation.
The occupant restraint module cover is typically designed to tear along predetermined lines to provide an opening for the expansion of the rapidly inflating air bag.
In view of the generally explosive nature of air bag inflation, a major problem with prior art module assemblies has been a tendency for the occupant restraint cover to detach from the housing during module opening and bag deployment. Should such disassembly occur, the occupant restraint cover or pieces thereof can act as projectiles and harm or injure the occupants.
In the past, various approaches have been proposed and/or employed in an attempt to overcome undesired detachment and/or breaking apart of the cover upon module opening and bag deployment.
For example, U.S. Pat. No. 4,989,897 discloses an apparatus for joining an air bag cover to an air bag housing, referred to therein as "a retainer." The patent discloses that a band of a strong material, such as steel, is fitted over the four side wall flanges of the cover whereby the side wall flanges are clamped to the peripheral wall of the housing. In a first embodiment of the invention, it is stated that the cover is retained on the housing due to the divergence of the peripheral wall of the housing. That the band is made of a strong material, such as steel, results in the band being well able to endure the stresses exerted during deployment. In an alternative embodiment, a steel plate is mounted to the outer surface of each flange of the air bag cover. Rivets (or nuts and bolts) pass through the steel plate, the flanges, and the peripheral wall of the housing whereby the flanges are firmly clamped by the steel plate and the peripheral wall.
In another approach, the plastic cover of the housing assembly is strengthened by embedding a band or mesh of a highly tear resistant material or fabric therein. For example, U.S. Pat. No. 5,064,217 discloses a cover, having an insert embedded therein, for use in conjunction with an inflatable air bag. The insert includes both a flexible net and a flexible reinforcing band assembly. The reinforcing band assembly includes a horizontal band which is coupled, such as by sewing, to the side portion of the net as well as vertical bands which are sewn to the horizontal band and to the side edges of the upper portion and/or the coupling portions of the net.
In general, a problem with such prior approaches is that they are typically relatively expensive to implement and can result in an undesirable, significant increase in the weight of the air bag assembly. Furthermore, such prior approaches tend to complicate the production process as they typically rely either on close fitting pieces or the inclusion of difficult and/or time consuming multiple additional production steps in the air bag assembly fabrication process in order to ensure and effect cover retention.